Directional radio system



Dec. 1Q, 1940. Y J. PLEBAN$K| 2,224,233

DIRECTIONAL RADIO SYSTEM Filed-May 5, 1938 3 Sheets-Sheet l OSCILLATOR ATTORNEY Dec. 10, 1940. J. PLEBANSKI DIRECTIONAL RADIO SYSTEM Filed May 5, 1938 5 Sheets-Sheet 2 INVENTOR- fiajef' rylebansfi ATTORNEY.

7 OSCILLATOR OSCI LLATOH Dec. 10,, 1940. .J,'PLEBANSKI 2,224,233

DIRECTIONAL RADIO SYSTEM Filed May 5, 195a a Sheets-Sheet a 94 smp t E 95 E 0,551 LLATO R sm p t 3 1 25 05C! L. LATOR .l. ,8 16 53 INVENTOR.

1; I ylebanslfi ATTORNEY.

Patented Dec. 10, 1940 I Jozef Plebanski; Warsaw, Poland; assignor t R dio Patents Corporation, New York, N. Y., a corporation of New York Application May 5, 1938, Serial No. 206,141 In Poland June 22, 1937 10 Claims.

' The present invention relates to directional radio systems and methods of operating the same such as for transmitting and/or receiving intelligence, for guiding moving craft, and for other 1 purposesj'well known.

' lAn 'object of the invention is the provision of a directional antenna system having a greatly improved cardioid type directional characteristic I The above and further objects and aspects compared with the directional patterns of similar type obtainable with the systems and methods known in the prior art. p

' Another object'is to'provide a directional radio system comprising spaced antenna units wherein the spacing of the individual units may be greatly reduced compared with conventional systems of or characteristic. I

this type for obtaining a given directional pattern A further object is to provide a radio beacon system simultaneously transmitting a plurality of different signals,' each signal being receivable in a different predetermined zone or sector only.

' Still a further object is the provision of a radio range beacon transmitting a characteristic signal within a narrow angular zone or sector.

Another" object is to provide asharplydefined narrow radio signal beam which can be adjusted in any desired direction.

' Another object is to provide a three-dimension radio beam system for guiding moving craft in both elevational and azimuthal directions.

Still a further object isto provide a radio range beacon and avisual left-right indicator cooperat ing therewith at the receiving end.

the invention will become more apparent from the following detailed description taken with reference to the accompanying drawings forming part of'this specification and wherein;

Figure l illustrates a'basic circuit constructed in. accordance with the invention comprising a pair of crossed loop aerials and an open or omnidirectional antenna for producing an improved cardioid' shapedpolar directional diagram, Figure 2 is a top view of a structure with centric loop aerials according to Figure 1,

COD-

Figure 3 shows the polar characteristic, or directional pattern obtained with a system according .to Figure 1,

,Figure 4 illustrates a modified systemof the type according to Figure 1,

Figure 5 shows a modification of an antenn system of the type shown in Figure 4,

, Figure Grepresents a directional antenna sys- .tem comprisingspaced antenna units of the according to'the invention,

type

Figures 7 and '8 show directional diagrams obtainable with antenna systems shown in Figure 6; Figure 9 illustrates a radio beacon system emv-' ploying the principles of the invention,-

Figure 10 shows the directional diagram explanatory of the function of the system shown in Figure 9 I c Figure 11 shows a modification of thesystern it according to Figure 9,

Figure 12 illustrates a pair of radio signal beacons accordingito Figures 10 and 11 for direc,- tion finding in both horizontal and vertical planes,

Figure 13 illustrates a radio beaconsystem ac cording to the invention with improved features embodied therein,

Figure 14 illustrates a receiver for visual leftright indication cooperating with a rangebeacon shown in Figure 13,

Figure 15 illustrates the invention as applied t point to point or secret communication.

Similar reference characters identify similar parts throughout the difierent views of the drawe v mgs.

Referring to Figures 1 and 2 wherein there is shown a transmitting system with an improved cardioid shaped directional characteristic;- items Ill and II representa pair of crossed loop aerials arranged with their planes perpendicular'to each other. The loops may be spaced or coaxial as shown in Figure 2. Both loops are shunted by tuning condensers l2 and I3 in series with in-jduction coils I4 and [5, respectively. 'The latter are arranged in inductive coupling relation;-

whereby the loop circuits are mutually coupled.

Numeral 16 represents anopen or omni-directional aerial connected to an inductance or loading coil I8 through a coupling condenser H. The upper terminals of the coupling coils l4 and I5 and the lower end of the loading coil I8 are connected to ground 20 as shown. The loop l0 and the Open antenna I6 are energized from an oscillator or source of carrier currents 2| through individual amplifying valves 23 and 22, respectively. To this end the anode of valve 22 is connected tothe upper side of the-antenna loading coil l8 through v e a coupling condenser 25, a coupling inductance 24 being inserted in the supplylead from the anode tothe positive pole of a high potential sup ply source indicated by the plus sign. Similarly I the anode of valve 23 is connected to the upper side of tuning condenser l2 for the loop through a coupling condenser 21, an output or coupling inductance 26 being inserted in the lead r m th a e Qfi is va qpth p iiv role of the high tension supply source. The loop ll receives its energy indirectly from the loop l0 through the coupling between coils l4 and [5. Any other coupling such as a. capacitative coupling may be employed between the loop circuits in place of the inductive coupling illustrated, as will be understood from the following.

If the two loop aerials l0 and H and the antenna I 6 are tuned to the frequency of the oscillations supplied by the source 2!, a directional radiation diagram or polar pattern will be obtained as shown in Figure 3. In the latter, a/a represents the well known figure of eight directional diagram for the loop it, b represents the circular diagram for the open or omni-directional antenna 86. Both diagrams combined result in the conventional cardioid shaped radiation pattern shown at 0. Curve d-d represents the figure of eight pattern for the second loop H receiving its energy indirectly from the loop I0 whereby the currents in the two loop circuits are phase shifted with respect to each other by exactly The radiation from the loop ll may be madegreater, equal, or smaller than the radiation from the loop it? such as by varying the number of turns in the two loops or in any other known manner. For the purposes of this invention, especially in connection with the arrangements illustrated in Figure 6, it is advantageous to provide for an increased radiation from the loop I I, preferably about twice or more compared with the radiation from the loop H], as shown in the example illustrated.

Taking into consideration the fact that the current in the loop ll (figure of eight diagram d-d) is in phase quadrature with respect to the current in the loop l0 (figure of eight diagram aa) and the open antenna (circle diagram 12), an over-all directional characteristic for the entire system is obtained as shown by the curve e in Figure 3. This curve represents a distorted cardioid having a substantially reduced non-receptive angle in the direction of the x-w axis compared with an ordinary cardioid such as shown at 0. At pattern of this type further differs from the conventional cardioid by the fact that the phases of the space waves radiated are no longer equal in all directions as in the conventional cardioid radiation pattern but differ from each other in the different directions. This type of'cardioid will therefore be referred to as a phase cardioid for the purpose of this specification .to distinguish from the regular cardioid pattern. The phases depend upon the sense or relative phase of the upper and lower circles of the pattern for the loop I 1. Thus, for instance, if the phase of the currents for the cardioid 0 (loop l0 and antenna i8) is assumed to be with respect to a zero phase or line and the phase of the current for the upper circle d for the loop II to be 90 with respect to said zero phase, then the phases of the space waves in different directions will be as shown by the solid arrows A, B, C, D, E, F, G, in Figure 3 for various directions. If the phase for the upper circle d of the diagram for the loop l i is reversed (270) then the phases of the radiated waves shall be as shown by the dotted arrows A,'B', C, D, E, F, G for the various directions.

There is thus shown and described by the invention a directional radio system comprising a first loop aerial and an open or omni-directional aerial to yield a cardioid shaped directional pattern and a second loop aerial with its plane or direction of maximum receptivity at right angles MarconieAdcock or any other known type.

to the plane of the first loop aerial and excited by currents being in phase quadrature to the currents in the first loo-p aerial and open antenna. By combination of the cardioid shaped diagram and the figure of eight diagram of the second loop aerial, a resultant phase cardioid diagram with substantially improved directional characteristics-is obtained.

In place of two crossed loops and an open antenna, a system comprising five open antennae such as wires may be employed to obtain a similar pattern in accordance with the invention, as illustrated in Figure 4. In the latter, the grounded aerial'wires 30-30, and 3 I3 I, may be of the The aerials 3fl30 are energized froma carrier source through a feeder line 33 including the primaries 3 3 and 35 of a pair of feeding transformers whose secondaries 36 and 37 are connected in series with the antenna wires. The antenna I6 is energized througha feeder 33 connected to a suitable tap point of the loading inductance l8. In order to effect the necessary 90 phase shift in the antenna 31-31, there are provided transformers 39 and all mutually coupling the antenna systems in a manner substantially similar to Figure 1. The feeder lines 33 and 38 may be connected to a transmitter or oscillator such as to separate power amplifying valves 22 and 23 as shown in Figure 1. There are further shown inductance coils 4| and 42. connected in series with the aerials 3| and 3!, respectively, for tuning the aerials to the same wave lengthto which aerials 30 and 30 are tuned by the inductances 31 and 36.

Instead of using two feeder lines, only one feeder -may be provided for energizing all antennae as shown in Figure 5. In the latter the grounded aerials 30-30 and 3|-3I are decoupled and energized by currents in phase quadrature from the carrier source through feeding transformers 39, 39 and 4 0, 43, respectively. The phase shift can be accomplished in any known manner such as by the insertion of phase shifting devices El and ill of any suitable construction in the feeders or by using feeders of different length. The open antenna IS in this case is fed from the same feeder 33. It is necessary however, that the open antenna be fed with currents of the same phase angle as the antenna 3i30. In order to improve the vertical radiation characteristic of the system, the individual antennae may be capacity-loaded by means of metallic top structures or conductors as shown at G'2fi2, Eli- 53 and 64, respectively. In this manner the radiation of sky waves is minimized resulting in reduction of fading due to interference between signals'absorbed from both earth bound and sky bound radiation at a receiving point.

Referring to Figure 6, there is shown an em bodiment of the invention app-lied toa directional antenna array, in the example shown comprising two antenna units each having a phase cardioid pattern of the type described previously. An advantage of an arrangement of this type is the fact that the spacing between the individual aerials which in the case of the conventional systems should be one-half the wave length can be considerably reduced to a distance of about onetenth of the wave length or less, while obtaining substantially the same directional characteristics originally obtainable with known arrangements employing substantially greater spacing distances. This makes it possible to construct directional transmitting aerials for the longer Wave lengths in a simple-and easy manner including the broadcast Waves from'200' to 500 meters wave length. 1

As iswell known, in order to meet the general requirements for broadcasting purposes and to avoid transmitting channel congestion, a solution has been found by using directional broadcasting aerials thereby providing a suflicient coverage for a densely populated surface area and at the same time eliminating interference in other regions. An obstacle to such a solution, however, has been the fact that the construction of directional aerials for wave lengths of the order of 500 meters is costly and complicated when using the known methods requiring spacing distances between the individual antenna units of the order of one-half of the wave length radiated; that is, spacings of the orderof 250 meters. Moreover, in order to obtain uni-directional transmission, reflectors have to be provided spaced from the main transmitting antenna by one-quarter of the wave length; that is, by distances of the order of about 125meters. By the present invention the above difficulties are substantially overcome by enabling a reduction of the spacing distance to as low as one-tenth of the wave length v 00 mounted at the top of the masts or towers 44 resulting in less bulky and expensive antenna structures. Thus,ior a wave length of 500 meters a spacing of the antenna units of only '75 meters will result in a pronounced directional or beam radiation characteristic as described more fully hereafter. 1

In order to obtain this object of the invention, two or more systems or units having a phase cardioid directional pattern are provided in spaced relation and fed from a common'carrier source or oscillator,

Referring to Figure. 6, such a system comprising two antenna units has been illustrated. Items 44 and 45 are two towers or masts'spaced by a distance I equal to about 0.15 of the wave length to be radiated. The masts are insulated from ground by insulators 46 and 41, respectively, whereby they constitute open aerials corresponding to the aerial IBinFigures 1, 4 and 5. For this purpose the masts 44 and 45 are connected to ground through tuning or loading coils 48 and 49, respectively, which latter are energized by a shielded feeder line 50 connected to the output of acarrier source or amplifier such as shown in the previous figures. Each of the mast antennae 44 and 45 has associated therewith a four-wire vertical antenna system of the type shown in Figures 4 and 5. The vertical antennae 52-52 and 53-53 for the mast 44 are suspended between supporting crossbars 55 and ground by means of insulators .54 as shown. Similarly the vertical wires 51-51 and 58-58 for the mast 45 are suspended between cross bars 60 and ground by means of insulators 59. The cross bars 55 and and 45 may be of conductive material to act as capacitative loadings for the open antennae similar to and for the purpose as pointed out above. The vertical antennae associated with each of the open mast antennae 44 and 45 are supplied with oscillating energy through a feeder line 56 from an amplifier or oscillator in a manner substanphases of the waves radiated are as shownat A, B, C, D, E, F, G in Figure 3 and if the antenna structure associated with mast 45 produces a phase cardioi type radiation characteristic as shown at g wherein the space phases of the radiated waves are as shown at A, B, C, D, E, F, G in Figure 3, then the resultant over-all radiation characteristic of the entire antenna system will be as shown at h in Figure 6, or as more clearly shown in Figure 7. In order to obtain such 'a characteristic the spacing I between the antenna units has to be only about 0.15 x (exactly 0.1475 A) instead of 0.5 A required in conventionalsystems. If the individual antennae 30-30, and 3l-3l and the antenna l6, Figure 4, are equal, the currents in 30-30 and I5 should be in phase and of such amplitude relation that the directional characteristic corresponds to (1-00 for the antennae 30-30 and to b for the open antenna I5, Figure 3. The current'in the antennae 3l-3I should be in phase quadrature and preferably have twice the amplitude of the current in the antennae 30-30. Alternatively, the spacing between the wires 3| -3 I may be greater than the spacing between the wires 30-30.

The arrangement according to Figure 6 is shown by way of example only and it is understood that many modifications are possible such.

as the employment of loop aerials in place of open wires. Furthermore, the masts 44 and 45 may be of non-radiating material and a special omni-directional or open antenna may be provided for each system and the units suspended between ground and a wire or other support connecting the two masts. The spacing l between the aerial systems or masts 44 and 45 may be further decreased. There is shown at i in Figure 8 a diagram for a spacing of .122 x and for a radiation from the antennae 3 l- 3 l two .and a half times greater than the radiation from the antennae, 30-30. By increasing the current in the open antenna, the diagram may be further improved as shown at a in Figure 8. An increased number of spaced antenna units may be provided to' further improve the directional characteristics as is understood. Moreover, the system may be used with equal advantage for receiving, in which case preferably shielded loop aerials or Marconi-Adcock systems are employed to prevent distortion of the directional characteristic by the downcoming component of electromagnetic radiation known as night error.

Referring to Figure 9, there is shown a radio signal beacon embodying the principle of the invention. The system illustrated is substantially similar to that shown in the previous figures, such as Figure 1. The carrier potentials impressed upon the loops I0 and l l and the open aerial l6 are simultaneously modulated in ac-- cordance with a first modulating signal such as a sinusoidal audible note sin pit while the carrier fed to the open aerial is additionally modulated .in accordance with a different signal or modulating note sin pzt. In the example illustrated, there is provided for this purpose a first modulating valve 10 having its grid excited by a potential varying according to the signal sin pit and being connected in shunt to the plate cir-' cuits of the amplifiers 22 and 23 in series with choke coils H and 12, respectively, according to the well known plate modulation method. Item 13 is a further highfrequency choke coil connected in the common lead between themodulating'tube 10and the. anodes, of amplifiers .22

and 23. In this manner the waves radiated by the loops in and H and the aerial I6 are modulated in accordance with a signal frequency in the example illustrated, a signal sin pit. Furthermore, the open aerial I8 is modulated additionally by means of a second modulating valve 14 having its grid excited by a different modulating signal in the example illustrated a sinusoidal potential varying according to sin mi, and having its anode connected to the anode of the amplifying tube 22 in series with a high fre-- quency choke coil 15. As is understood, any other well known modulating system may be employed for the purpose of the invention. An arrangement of this type may be designed and adjusted in such a manner that the modulating signal sin pzt applied by the valve '14 is transmitted only within a narrow angle a as shown in the diagram of Figure 10; whereas the modulating signal sin plt applied by the valve I0 is transmitted in all the remaining directions in accordance with the phase cardioid e.

This is further understood from the following: by assuming that the loop ID in Figure 9 has a characteristic a-a, that the open aerial I6 has a characteristic 1) and that the loop H has a characteristic d-d as shown in Figure 3, and that furthermore the loop currents are in phase quadrature as described, the field strength at a point in space whose connecting line with the transmitter forms an angle 5 with the axis :ra: in Figure 10 may be defined by the following theoretical expression:

e=A1 sin wt+B1 sin pit sin wt radiation from open antenna l6 modulated according sin put (A1 sin wt-l-Bi sin pit sin wt)K1 cos 3 radiation from loop H] modulated according sin pit +(A2 cos wt-l-Bl sin pit cos wt)K2 sin 9 radiation from 100p H modulated according sin plt +A2 sin wt-l-Bz sin pzt sin wt radiation from antenna l6 modulated according to sin pat wherein A1 and A2 are theamplitudes of the carriers or unmodulated components, and B1 and B2 are the amplitudes of the modulated components of the carrier currents inthe separate antennae.

In the direction 5:0 (axis zit-fir); assuming K1=1, the first six terms will disappear and the field strength found to be as follows:

e:A2 sin wt-l-Bz sin pQt-l-sin wt From the above it is seen that in a system of this type, the modulating signal having a frequency 292/211- will be heard only within a narrow transmitting angle, in practice being only about 1 to 2 degrees. In all other directions, the second signal having a frequency p1/21r will be heard. This i further explained as follows. ince both loop aerials l0 and H and the open antenna it are energized by the carrier from oscillator 2| and modulated according to a modulating signal sin pit through valve 10 and choke coils H and 12, the directional characteristic obtained will be of the phase cardioid type as explained hereinbefore resulting in a narrow angle or of no emission. If therefore the currents in the open antenna are now additionally modulated according to a modulating signal sin pzt through valve 14 and assuming the carrier in the open antenna to be greater than in the other antennae (e. g., A1+A2) then this open antenna modulation (according to sin 272i) will be radiated in all directions including the angle a. In the direction other than covered by the angle on, however, the

modulation signal according to sin pet will be drowned out or banketed by the stronger modulation, leaving only the angle on for eiTective radiation of the signal modulation according to sin 10215. In Figure 10 the carrier and modulation according to sin pit for the different directions are represented by the curve e and the desired carrier and modulation by the circle K.

The transmitting angle a for the first signal will become extremely small if A2 is made small in relation to A1 in the above expressions. In Figure 10 there is shown by the circle is the carrier A2 as compared with the phase cardioid e showing the amplitudes of the carrier for all other directions. If A2 is made zero which can be easily accomplished by adjusting the carrier currents in the loop I0 and the open aerial l6 in the unmo'dulated condition in such a manner as to obtain a pure cardioid diagram, only the two modulated side bands will be transmitted in the direction m:0 within the angle a for the signal frequency p2/21r with the carrier being eliminated. As is understood, actually the signal pz/21r is transmitted in all directions, but is cancelled by the substantially stronger signal p1/21r except within a narrow sector or angle.

A system of the above described type is Well suited as a radio range beacon for guiding ships, aircraft, or other vehicles along a fixed route by defining a sharp zone wherein a predetermined signal is received. As an example for this purpose, the valve 10 may be modulated by a message identifying the name of the transmitting beacon while the valve 14 may be modulated in accordance with a diiferent characteristic signal such as a definite audible note of a thousand cycles or any other desired frequency. Thus, a pilot will hear the name of the beacon in substantially all directions of travel of his craft, but will receive the characteristic signal in a predetermined direction only corresponding to a predetermined course towards or away from the transmitting beacon.

In Figure 11 there is shown a system of the type according to Figure 9 for producing a radio signal beacon whose direction can be adjusted within 360 in a simple and easy manner by varying the phase of the carrier current fed to the open antenna l6. To accomplish this, in the example illustrated, there is shown a phase shifting arrangement connected between the source of carrier current 2| and the amplifier 22 energizing the open aerial I6. This phase shifting device comprises an induction coil shunted by a condenser 19 to form a tuned circuit connected to the source 21. There are further shown a pair of crossed induction coils BI and 82 having their planes arranged fixedly'and mutually perpendicular to each other. The induction coil 8! has connected thereto a tuning condenser 83 in series with a coupling coil 86 and similarly the coil 82 has connected thereto a tuning condenser 8'2 in series with a coupling coil 85. The coils and 86 are arranged in inductive coupling relation in such a manner that if the circuits of both coils are tuned to resonance with the impressed carrier signals, the phase of the carrier potential derived from one of the tuned circuits, in the example illustrated the circuit of coil 82 impressed upon the grid of the modulating tube 22 through coupling condenser 81 and grid leak resistance 88, may be varied between 0 and 360 by adjusting the relative position between the coil 86 on the one hand and the crossed coils 8| and 82 such as described in detail in my copending applicationjSerial No. 133,793 filed March 30, 1937, entitled Electrical systems.

In this manner, the signal beam (angle 1 may be rotated through an angle, of 360 by rotating the crossed coils 8| and 82 ina most simple'and easy manner. In an arrangement of this type, it is preferable to employ loops l0, and II of substantially equal radiating strength. As is understood, anyother phase rotating device may-be employed for the purpose'of the invention, although the system shown has the advantage of general simplicity and efiiciency. As is. understood the valves 22 and 23 may bemodulated in a manner described previously to obtain a signal beam radiation. To this effect, a first modulating valve 10 having its grid excited by apotential ivarying according to the signal sin pit is connected in shunt to the plate circuit of amplifier 23 in series with a low frequency choke coil 12 and a high frequency choke coil 13, and a second modulating valve 14 having its grid excited by a different modulating signal varying according to signal sin 1172f is connected in shunt to the 'platecircuit of amplifier 22 and in series with a high frequency choke coil 15; amplifier 22 is connected through a low frequency coil H with one end of the high frequency choke coil 26 1 It will be appreciated that in this way the oscillatory energy of the principal character as to frequency and otherwise delivered by oscillator 2| is modulated with the signal sin pit and sin pat, respectively, according to the'well known plate modulation method. The signals sin pit and sin mt can be substituted by any desired other form of signals.

A system of the'type according to Figure 9 is also well suited for transmitting interlocking signals such as the letters 11. and a according to the well known Morse code.

In the latter case, the valve 14 may be keyed according to. the letter a (dot followed by a dash) and the valve-10 may be keyed in accordance with the letter 11 (dash followed by adot), both letters interlocking so as to merge into a continuous dash if received with .9 and-11 may be combined, one designed for defining a signal beam in a vertical plane, thereby enabling direction finding or guidance .of moving craft in three dimensional space for blind landing and other uses. Thus, e. g., if one of the systems works-with a note of say 400 cycles and the other with a note of 1000 cycles, it can be shown that predetermined zones are defined in a vertical plane at right angle to the transmission of the beams enabling a pilot to guide his craft in both azimuthal and elevational directions.

A 11 1111111 1 this type is illustrated in Figure 12 Inthe latter the loops i0 and II andthe open aerial l6 fed from the source 2| through valves 23 and'22 are provided to. define a signal beacon in a horizontal or azimuthal plane in themanner described hereinbefore. To this end, both loops and the open aerial are modulated in accordance with a first signal note sin pit through a compo'site double section modulating valve 9| connected to the' anodes-of amplifiers 22 and 23 through choke coils 93, and 92-, 94, respectively. The open aerial is additionally modulated in accordance with a signal note sin pzt' by the aid of a modulating valve 90 connected to the anode of valve 22 in a manner similar as described hereinbefore. The tuning of and the couplingmeans between the loops l0 and I I are'not shown for purpose of simplicity, both having been previa central induction coil I06 and opposite horizontal radiating wires I06 and I06". One of the loop aerials I04 or I05 is supplied with carrier energy through a valve amplifier 96 having its grid excited by the carrier source 2!, coupling condenser 98 and a tuned circuit comprised'of an induction coil I00 shunted by a condenser 99, the leads I90 from the tank circuit 99, being connected to suitable tap points on the loop inductance. The loops 10, II and [04,105- are tuned and mutually coupled with each other in exactly the same manner as previously described but not shown for the sake of simplicity of illustration. Similarly, the dipole antenna is supplied with carrier energy through an amplifier valve 91 also excited by the carrier source 2|, a

coupling condenser I01 and a tuned circuit com-.

prising an inductance coil I09 shunted by' condenser I08. Thecarrier currents impressed upon the loops H74 and I05 and the dipole antenna I06 are modulated in accordance with the signal note sin pzt by the aid of a double section-modulating valve H5 having its anodes connected tothe anodes of the valves 96 and 91 through choke coils I I6, Band H1, H9, respectively, while the dipole antenna'is modulated additionally according to the signal note sin pit by means of amodulating valve ll3connected to the anode of valve 91. Further details, such as coupling between figures and are therefore not'repeated for simplicity of illustration.

In a system of this type definite signal zones are created in aplane at right angles to the direction ofthe signal beacons as follows, assuming that the signalbeacon in one plane such as the horizontal plane-has a 4100 cycle note keyed in interlocking relation according to the letters a and n in the manner as described hereinabove and that the signal beacon in the other (vertical). plane has a 1000 cycle note similarly keyed-according to the letters a and n. V 1

The signals are transmitted on the same wave length or carrier so that a simple receiver can be employed. There is thus defined a path or 'xbeam by the intersection of both signal beacons in three-dimensional space which may correspond to the gliding'path'of an aircraft for efiectaxes horizontally,th e dipole antenna comprising .loops, etc., are substantially the same as shown and described in connection with the previous ing a blind landing and which can be easily identified by the pilot when receiving the letter a on both notes simultaneously; that is, when hearing a pure double note interrupted according to the letter a without any background. The above table indicates a continuous dash by d at either 400 or 1000 cycles or with both notes received simultaneously.

Systems of the type according to Figures 9, 11 and 12 are subject to left-right ambiguity which can be eliminated by an improved arrangement shown in Figures 13 and 14. In Figure 13 the loop I 0 and the open antenna I6 are energized by carrier currents in quadrature phase relation to the current fed to the loop II and similarly the modulating currents for the loop I0 and the antenna I6 are in phase quadrature to the modulating current for the loop I I. To this end there is connected to the carrier source 2I a transformer I having its secondary shunted by a tuning condenser and a pair of series networks one of which comprises a non-reactive or ohmic impedance I2I and a condenser I22. Similarly the other network comprises a condenser I23 in series with a resistance I24. The potential developed at the junction between resistance IN and condenser I22 is impressed upon the grids of a pair of amplifier valves I and I26, the former serving to energize the antenna I6 and the latter energizing the loop aerial I0. Similarly the potential at the junction between the condenser I23 and resistance I24 is impressed upon the grid of valve I21 serving to excite the other loop aerial I I. Since the potentials at these junction points and ground are at a mutual 90 phase difference, it is seen that the antenna I6 and the loop aerial III are excited by carrier currents which are in quadrature phase relation to the currents exciting the loop I I.

In addition, the carrier oscillation fed to the open antenna I6 and to the loop aerial I0 on the one hand and the loop antenna II on the other hand are modulated by quadrature modulating currents. For this purpose the source of modulating currents I28 has connected thereto a transformer I29 having its secondary shunted by tuning condenser and a pair of series networks, the network comprising a resistance I30 and a condenser I3I and the second network comprising a condenser I32 and a resistance I33. The potential developed at the junction between the condenser I32 and resistance I33 is impressed upon the grids of a pair of modulating valves I34 and I35 serving to modulate the carrier currents supplied by the amplifier valves I25 and I26 and impressed upon the open antenna I6 and loop aerial I0, respectively. Similarly the potential developed at the junction between the resistance I30 and condenser I3I is impressed upon the grid of modulating valve I36 serving to modulate the currents supplied by the amplifier valve I2! feeding the second loop aerial I I.

It can be shown that in a system of the aforedescribed type wherein the radiation of the open antenna I6 is slightly higher than the radiation from the loop aerial II], a deviation of the vessel or aircraft to the right will cause elimination (within the zone 12 according to Figure 10) of one of the modulated signal side bands, such as the upper side band, while deviationto the left will result in elimination of the other or lower modulated side band according to the example chosen. By using on the vessel or aircraft a receiver including two resonant circuits one of which is detuned slightly above and the other is detuned slightly below the carrier frequency (or of the intermediate frequency in case of a superheterodyne receiver) with suitable rectifiers connected thereto in differential arrangement, the deviation can be indicated by means of a zero center indicating instrument.

A simple receiving circuit of this type is shown in Figure 14. In the latter, I40 represents a receiving antenna connected to ground through a coupling condenser MI and the primary of a tuned input transformer I42. The secondary of the latter is arranged to excite the grid of an amplifying valve I43 having a tuned circuit I44 connected in its output. The circuit I44 is coupled with two tuned circuits I45 and I46 each slightly detuned oppositely relative to the tuning of the circuit I44 (carrier frequency). The circuits I45, I46 are connected in series with diode rectifiers I41, I48, load resistors I49 and I50, the latter being shunted by smoothing capacities I5I, I52. Numeral I53 represents a zero center type indicating instrument showing the deviation of a craft to the left or right from its true course as determined by a signal beam of the type shown in Figure 13.

For blind landing, two groups of detuned circuits will be required. One group for the horizontal bearing indication and another for indicating the vertical bearing. In this case one indicating instrument may serve to show the horizontal course and a further instrument to show the vertical course. Alternatively a combined instrument can be employed as is customary in systems of this type. Furthermore, the two groups of detuned circuits should diifer only by the degree of detuning as one group should be sensitive only for one (such as the lower modulating frequency) and to the side bands produced by this frequency, while the other group should be sensitive for the other (such as a higher modulating frequency). Both beams that is, both for horizontal and Vertical bearing indication may operate on the same wave length which may be of the order of 1000 meters or any other desired value.

Thus, supposing for instance that the two beacons, that is both the horizontal and vertical beacon to operate on 900 meters wave length and one (e. g., the vertical beacon) to be modulated by a 1000 cycle note and the other (i. e., the horizontal beacon in the example) to be modulated by a 5000 cycle note, two channels may be provided in the receiver for the intermediate frequency signals of say 130 kc.+1 kc. and 130 kc.+5 kc., respectively, with relatively detuned circuits in each as shown at I45, I46, Figure 14. The instrument in this case may be a double or twin instrument having their pointers arranged vertically and horizontally and each having its moving coil connected to one pair of detuned circuits.

Referring to Figure 15, there is illustrated a further application of the invention for point to point or secret communication. For this purpose there are provided at a first point (station 0) two aerials one of which has a phase cardioid radiation pattern N while the other may be an omni-directional aerial or a directional aerial with a characteristic P whose axis coincides with the direction of zero radiation or receptivity of the first aerial. Similarly there are provided at a distant point (station p) two aerials, one with a phase cardioid pattern 0 and the other with a pattern Q and oriented in the direction of the station 0 as illustrated. Thus, as is seen, if the second aerials at both stations are of the omni- "directional type in place of directional. aerials (patterns P and Q as illustrated) and if different modulating signals are transmitted on the same wave length by the directional aerials (phase cardioids N and O) and by the omni-directional aerials by means of arrangementssimilar to Fig ure 9, communication for the desired signals may be carried out only in the direction 1 between the stations and p; in all other directions the de- 1 sired signal is drowned or blanketed by the signals according to the phase'cardioidi radiation claims.

in a manner similar to the operation described in connection with Figure 9. This effect, as will be evident iromthe .above, is further improved 'by'using directional aerials with patterns P and Q in place of omni-directional aerials oriented in the manner'shown. I

It will be apparent from the above that the invention is not limited to the specific arrangement of parts and elements shown and disclosed herein for illustration but that the underlying idea and principle of the invention aresusceptible ofv numerous modifications and variations differing from the embodiments described and illustrated and coming within the broader scope and spirit of the invention as defined "in the appended The specification and drawings are therefore to be regarded in an illustrative rather, than in a limited sense.

I claim:

1. A directional radiosystem comprising a plu- I rality of spaced antenna units, eachunit comp'risingan open antenna and a pair of directional antennae having figure of eight characteristics arranged at an angle of 90 relative to each other, the phases of the figure of eight characteristics of "corresponding directional antennae in successive units being reversed by 180, means for causing oscillatory energy in the open antenna and 1 one of the directional antennae in each unit to be in phase-quadrature with the energy in the remaining directional antenna of'each unit, and a common operating circuit connected to all of said antennae." 2. A radio transmitter comprising an open an tenna, a pair of directional antennaehaving figure of eight characteristics oriented at a sub-- stantiallyright angle relative to each other, a source of oscillatory energy,- means for feeding energies of substantially equal phase relation from said source to said open antenna and to one of said directional antennae and for feeding to said other directional antenna energy in quadrature phase relation to said first energy, means for modulating the energies fed to said .open antenna and said directional antennae in accordance with a first modulatingsignal, and further means for additionally modulating the energy fed to "said open antenna in'accordance with a second 3 different modulating signal. I

3. In a radio system-as cla med inclaim 2, means for-variably adjusting the phase of the energy fed to said open antenna.

f 4. A radio transmitter comprising an open an :tenna, 'a pair of loop antennae arranged with their planes forming substantially a right angle,

.a source of carrier current, resonant circuits connected to saidloop antennae, inductive coupling ulating source.

character.

a first modulating signal and further means for means connecting said resonant circuits, means for feeding energies from said source to-said open antenna and to one of said loop antennae, means i; 5 for modulating said energiesin' accordance with modulating the energy fed to said open antenna in accordance with a second different modulating signal. 7

5. In a radio transmitter as claimed in claim 4, including means for adjusting the phase of the. carrier current'fed to said open-antenna.

6. A directional radio'trans-mitter comprising" an open antenna, a. pair of directional antennae having figure of eight characteristics oriented at substantially a right angle relative to each other, a source of carrier ener y, means for feeding energies in like phase from said source to saidopen antenna and one of said directional antennae, further 'meansfor feeding energyfrom said source to said, other directional antenna in phase quadrature relative to said first energies, a source of modulating signals, means for modulating the energy fed to said open antenna and to said first directional antenna in accordance with said modulating signals, and further means for modulating theenergy fed-to said other directional antenna in accordance with modulating signals in phase quadrature to said first mOdH-f lating signals.

'7. A directional radio transmitter comprising an open antenna, a'pair of 'loop antennae 'arranged with their planes forming substantially a for feeding energies in phase quadrature relation from said sour-ceto said, open antenna and one of i said loop antenna and to said other loop antenna,

respectively, a source of modulating signals, and

. further means for modulating each of said energies in accordance with signal components in quadrature phase relation derived from said mod- 8. A directional 'radi system comprising two spaced antenna units, each unit comprised of an having figure of eight characteristics oriented at a substantially right angle relative to each other, means for feeding oscillatory energies of i right angle, a source of oscillatory energy, means open antenna and a pair of directional antennae likeprincipal. characteristic and substantially in phaseto the open antenna and one of the directional antennae and shifted in phase by about. 90 to the other directional antenna of each of said units, means for modulatingsaid oscillatory energies fed to alla'ntennae of one and to the open antenna of the other of said units in accordance with a first signal, and said oscillatory energiesfed to all antennae of said other'unit and to the open antenna of said first mentioned unit in accordance with a second signal.

9. In a system as described in claim 8 in which we each of said units comprises directional antennae with their directions of maximum receptivity in acommon plane, said planes, of said units being arranged substantially perpendicular to each I other- 1 I 10. In a'system as described in claim 8, said first and second signalsbeing of interlocking JQZEF PLEBANSKI. 

